Ventilation of confined spaces such as dwellings, buildings, cars, etc, where living and or industrial activities take place, is a common practice. The products of metabolic processes and of industrial activities generate substances such as water vapor, carbon dioxide, odors, dust, smoke, etc., which, if allowed to build-up in the confined space would render its atmosphere unsuitable for human occupancy.
This situation is avoided by extracting a certain amount of the indoors air and replacing it with uncontaminated outdoors fresh air.
The concentration of the contaminants may thus be kept at levels compatible with the desired or required degrees of comfort and safety.
The flowrate of indoors air extracted will depend on the rate of generation of the contaminants and on their desired or required concentration in the confined space.
The influx of outdoors air into a ventilated space will introduce an extra heating or cooling load, depending on the yearly seasons, due to the difference in temperatures between the outdoors and indoors.
In the winter an extra heating load is required to raise the temperature and humidity of the cold and dry air inflow to the levels maintained in the confined space. During the summer and extra cooling or refrigeration load is required to decrease the temperature and humidity of the incoming hot and humid air. These extra heating and refrigeration loads are a substantial part of the total ventilation load and cause an extra expenditure of fuel and or electric power.
Air to air heat exchangers have been used with limited success, to recover a portion of the extra heating load above mentioned. Beside their relatively low recovery efficiency, these devices have no capabilities for substantially increase or decrease the humidity of the air streams.